The present invention relates to a photocatalyst exhibiting high photoactivity. More particularly, the present invention relates to photocatalytic particles and a photocatalytic powder exhibiting sufficient photocatalytic properties when irradiated with light from a practical light source of low quantity of light, such as a fluorescent lamp; a material containing the particles or powder, such as an organic polymer composition, a slurry, a coating agent, or a film exhibiting photocatalytic property and hydrophilicity; and a product containing the particles or powder.
Conventionally, titanium oxide has been widely used in practice as a typical photocatalyst. Titanium oxide absorbs UV rays having a wavelength of about 400 nm or less, to thereby excite electrons thereof. When the resultant electrons and holes reach the surfaces of titanium oxide particles, the electrons and holes are combined with oxygen or water, thereby generating various radicals. The resultant radicals exert oxidizing effect to thereby oxidize and decompose substances adsorbed on the surfaces of the particles. Fundamentally, a titanium oxide photocatalyst functions as described above. Studies have been carried out on environmental purification utilizing such photo-functional properties of titanium oxide ultrafine particles, such as antibiosis, deodorization, antifouling, air cleaning, and water cleaning.
In order to improve the photocatalytic properties of titanium oxide particles, the following means have been proposed.
(1) Reduction of Particle Size
Reduction of particle size is very effective for preventing recombination of generated electrons and holes.
(2) Enhancement of Crystallinity
Enhancement of crystallinity is effective for increasing the rate of diffusion of generated electrons and holes toward the surfaces of particles.
(3) Separation of Electrons and Holes
Generated electrons and holes are separated from each other, to thereby increase the ratio of electrons or holes which reach the surfaces of particles.
(4) Regulation of Band Gap
When a band gap is reduced (i.e., maximum absorption wavelength is increased) through, for example, incorporation of small amounts of impurities, percent utilization of a light source containing small amounts of UV rays, such as sunlight or a fluorescent lamp, can be increased.
In order to attain the aforementioned means (4), recently, various studies have been performed on a photocatalyst which responds to visible light.
For example as disclosed in JP-A-9-262482 (the term xe2x80x9cJP-Axe2x80x9d as used herein means xe2x80x9cunexamined published Japanese Patent Applicationxe2x80x9d), anatase-type titanium dioxide of high catalytic activity is modified through ion implantation by use of a metal such as chromium (Cr) or vanadium (V), so as to shift the maximum light absorption wavelength of the titanium dioxide to a longer wavelength, thereby causing the titanium dioxide catalyst to function under irradiation with visible light. However, the aforementioned ion implantation by use of a metal requires a large, expensive apparatus and is industrially impractical.
JP-A-2001-72419 discloses titanium oxide designed such that, in the case where the half-width of the peak of titanium of the titanium oxidexe2x80x94which is present within the bond energy of 458 to 460 eVxe2x80x94is measured four times by means of X-ray photoelectron spectroscopy, when the average of the half-widths of the peak of titanium at the first and second measurement is represented by xe2x80x9cA,xe2x80x9d and the average of the half-widths of the peak of titanium at the third and fourth measurement is represented by xe2x80x9cB,xe2x80x9d the index X (i.e., B/A) becomes 0.97 or less. However, since powder of the titanium oxide has low activity and is colored, application of the titanium oxide powder is limited. Therefore, the powder is not suitable for use in a coating material which requires transparency.
Conventional photocatalysts which respond to visible light are difficult to use in practice, since they require a strong light source such as a xenon lamp in order to exhibit their catalytic properties sufficiently. Therefore, it would be greatly advantageous to provide a photocatalyst which exerts sufficient effects when irradiated with light from a conventional inexpensive light source; for example, a light source used in a room, such as a day white fluorescent lamp.
International Patent Publication WO94/11092 discloses a method for treating bacteria or malodorous substances by applying a photocatalytic thin film containing a semiconductor of, for example, titanium dioxide onto the inner wall of a sickroom or a residential space. However, the publication does not disclose a method for imparting activity to titanium dioxide and the photocatalytic activity of particles of the titanium dioxide. Provided that typical titanium dioxide is employed, when the photocatalytic thin film is irradiated with light from a light source containing small amounts of UV rays, such as a fluorescent lamp, the activity of the thin film is expected to be lower than that of the aforementioned visible-light-response-type photocatalyst.
Attempts to utilize photocatalytic properties of titanium oxide fine particles have led to proposals of a method of kneading titanium oxide fine particles into an easily handled medium such as a fibrous material or a plastic formed article, and a method of applying the fine particles to the surface of a substrate such as cloth or paper. However, not only harmful organic substances or environmental contaminants, but also media such as fiber, plastic, and paper are easily decomposed and impaired by the strong photocatalytic action of titanium oxide, and, in view of durability, this stands as an obstacle to practical use. Also, since titanium oxide fine particles are easily handled, a coating material prepared by mixing titanium oxide fine particles and a binder has been developed. However, an inexpensive binder exhibiting the durability sufficiently high to overcome the problem (obstacle) of action on the media has not yet been found.
JP-A-9-225319 and JP-A-9-239277 disclose a technique of preventing and suppressing the deterioration of a resin medium or a binder that would otherwise occur because of the strong photocatalytic action of titanium oxide particles, where there is proposed, as means therefor, a method of bearing a photoinactive compound containing an element such as aluminum, silicon, or zirconium on the surfaces of titanium oxide particles such that the compound assumes a form of archipelago with steric hindrance to thereby suppress the photocatalytic action. However, this method is disadvantageous in that, although the photoinactive compound is supported so as to form an archipelago form, a portion subjected to the strong photocatalytic activity of titanium dioxide is present at a specific site of the resin medium or binder.
JP-A-10-244166 proposes photocatalytic titanium oxide prepared by coating the surface of titanium oxide with porous calcium phosphate. However, in this case, as has been pointed out, the photocatalytic performance decreases because of the coating film; i.e., the calcium phosphate layer.
International Patent Publication WO99/33566 discloses a titanium dioxide fine particle powder where a porous calcium phosphate coating layer is formed at least on a portion of the surfaces of titanium dioxide fine particles, and an anionic surfactant is present in the interface between the layer and the surface of the fine particles.
With respect to a slurry containing titanium oxide having photocatalytic activity, JP-A-10-142008 discloses an anatase-type-titanium-oxide-containing slurry obtained by subjecting a titania sol solution, a titania gel, or a titania solxc2x7gel mixture to heat treatment and pressure treatment in a closed container, and then to dispersion using ultrasonic waves or stirring.
JP-A-11-343426 discloses a photocatalytic coating material having excellent dispersion stability, which is a photocatalytic coating material containing titanium oxide and silica sol in a solvent, where the titanium oxide has a Raman spectrum peak in the range from 146 to 150 cmxe2x88x921, and anatase-type titanium oxide accounts for 95 mass % or more of the titanium oxide.
As described above, although several techniques have been disclosed, there have not yet been provided, in an industrially useful manner, photocatalytic powder and slurry which exhibit photocatalytic properties and which satisfy requirements for both durability and dispersion stability when used in combination with an organic material.
In view of the foregoing, an object of the present invention is to provide photocatalytic particles and a photocatalytic powder exhibiting sufficient photocatalytic properties when irradiated with light from a practical light source of low quantity of light, such as a fluorescent lamp; a material containing the particles or powder, such as an organic polymer composition, a slurry, a coating agent, or a film exhibiting photocatalytic property; and a product containing the particles or powder. The composition and the film undergo a minimum level of coloring, and the film has high transparency.
Another object of the present invention is to provide a photocatalytic powder which exhibits excellent dispersion stability without impairing the photocatalytic property of titanium dioxide, and which has excellent industrial applicability; a slurry containing the powder; a polymer composition containing the powder; a coating agent containing the powder; a photocatalytic formed article containing the powder; and a photocatalytic structure containing the powder.
The present invention provides a photocatalytic powder and a photocatalytic slurry which exhibit excellent photocatalytic property, durability, and dispersion stability when applied to the coating of a material such as fiber, paper, or plastic; when kneaded into such a material; and when used in a coating material composition.
The present inventors have performed extensive studies and have attained the aforementioned objects by forming photocatalytic particles exhibiting high activity even when irradiated with light from a light source of low quantity of light, and by inventing a photocatalytic powder and a slurry containing the powder, the powder being characterized in that a polybasic acid salt containing at least one species selected from the group consisting of alkaline earth metals, transition metals, and Al is present on the surfaces of the aforementioned titanium dioxide fine particles of high activity.
Accordingly, the present invention provides the following.
(1) Photocatalytic particles characterized in that, in 5 L of dry air containing 20 ppm acetaldehyde, after 3.5 g of the particles that have been uniformly applied onto a plane having a diameter of 9 cm are irradiated with light for one hour by use of a day white fluorescent lamp such that the intensity of UV rays of 365 nm is 6 xcexcW/cm2, percent decomposition of the acetaldehyde is at least about 20%.
(2) Photocatalytic particles according to (1), wherein the percent decomposition is at least about 40%.
(3) Photocatalytic particles according to (2), wherein the percent decomposition is at least about 80%.
(4) Photocatalytic particles according to any one of (1) through (3), which comprise titanium dioxide.
(5) Photocatalytic particles according to (4), wherein the titanium dioxide has a BET specific surface area of about 10 to about 300 m2/g.
(6) Photocatalytic particles according to (5), wherein the titanium dioxide contains an anatase-type crystal form.
(7) Photocatalytic particles according to (5), wherein the titanium dioxide contains a brookite-type crystal form.
(8) Photocatalytic particles according to (5), wherein the titanium dioxide contains a rutile-type crystal form.
(9) Photocatalytic particles according to (5), wherein the titanium dioxide contains at least two crystal forms selected from among anatase, rutile, and brookite.
(10) Photocatalytic particles according to any one of (6) through (9), which are composite particles containing the titanium dioxide and photocatalytically inactive ceramic.
(11) Photocatalytic particles according to (10), wherein the photocatalytically inactive ceramic is present partially on the surfaces of titanium dioxide particles.
(12) Photocatalytic particles according to (10) or (11), wherein the photocatalytically inactive ceramic is a salt containing at least one species selected from the group consisting of an alkaline earth metal, a transition metal, and Al.
(13) Photocatalytic particles according to (12), wherein the alkaline earth metal is at least one species selected from the group consisting of Mg and Ca.
(14) Photocatalytic particles according to (12), wherein the transition metal is at least one species selected from the group consisting of Fe and Zn.
(15) Photocatalytic particles according to (12), wherein the salt containing an alkaline earth metal or a transition metal is selected from among a phosphate, a condensed phosphate, a borate, a sulfate, a condensed sulfate, and a carboxylate.
(16) Photocatalytic particles according to (15), wherein the condensed phosphate is at least one salt selected from the group consisting of a pyrophosphate, a tripolyphosphate, a tetrapolyphosphate, a metaphosphate, and an ultraphosphate.
(17) Photocatalytic particles according to (10) or (11), wherein the photocatalytically inactive ceramic is at least one species selected from the group consisting of an Si compound, an Al compound, a P compound, an S compound, and an N compound.
(18) Photocatalytic particles according to any one of (10) through (17), wherein the composite particles have a BET specific surface area of about 10 to about 300 m2/g.
(19) Photocatalytic particles according to any one of (1) through (18), which have an isoelectric point of about 4 or less obtained on the basis of a zeta potential as measured by means of an electrophoresis light-scattering method.
(20) A photocatalytic powder comprising photocatalytic particles as recited in any one of (1) through (19).
(21) An organic polymer composition comprising photocatalytic particles as recited in any one of (1) through (19).
(22) An organic polymer composition according to (21), wherein the organic polymer of the composition is at least one species selected from the group consisting of a thermoplastic resin, a thermosetting resin, a synthetic resin, a natural resin, and a hydrophilic polymer.
(23) An organic polymer composition according to (21), which is at least one species selected from the group consisting of a coating material, a coating composition, a compound, and a masterbatch.
(24) An organic polymer composition according to any one of (21) through (23), which contains the photocatalytic powder in an amount of about 0.01 to about 80 mass % on the basis of the entire mass of the composition.
(25) A photocatalytic formed article which is formed from an organic polymer composition as recited in any one of (21) through (24).
(26) A photocatalytic formed article according to (25), which is at least one formed article selected from the group consisting of fiber, film, and plastic.
(27) A product which is produced from a photocatalytic formed article as recited in (26).
(28) A product comprising, on its surface, photocatalytic particles as recited in any one of (1) through (19).
(29) A product according to (27) or (28), which is at least one member selected from the group consisting of building materials, machinery, vehicles, glass products, electric appliances, agricultural materials, electronic apparatus, tools, tableware, bath products, toiletry products, furniture, clothing, cloth products, fibers, leather products, paper products, sporting goods, futon, containers, eyeglasses, signboards, piping, wiring, brackets, sanitary materials, and automobile parts.
(30) A slurry comprising photocatalytic particles as recited in any one of (1) through (19).
(31) A slurry comprising photocatalytic particles, wherein a powder obtained by drying the slurry is photocatalytic particles as recited in any one of (1) through (19).
(32) A slurry according to (30) or (31), which contains water as a solvent.
(33) A slurry according to (30) or (31), which contains photocatalytic particles in an amount of about 0.01 to about 50%.
(34) A slurry according to (30) or (31), which has a pH of about 4 to about 10.
(35) A slurry according to (34), which has a pH of about 6 to about 8.
(36) A slurry according to any one of (30) through (35), wherein, when the slurry contains the photocatalytic particles in an amount of 10%, the slurry has a transmittance of at least about 10% as measured at a wavelength of 550 nm and an optical length of 2 mm.
(37) A slurry according to (36), which has a transmittance of at least about 30%.
(38) A coating agent comprising photocatalytic particles as recited in any one of (1) through (19) and a binder, which is to be formed into a film exhibiting photocatalytic property.
(39) A coating agent comprising a slurry as recited in any one of (30) through (37) and a binder, which is to be formed into a film exhibiting photocatalytic property.
(40) A coating agent according to (38) or (39), wherein the binder contains an organic compound.
(41) A coating agent according to (40), wherein the organic compound is at least one species selected from the group consisting of acrylsilicon, polyvinyl alcohol, melamine resin, urethane resin, acrylurethane, celluloid, chitin, starch sheet, polyacrylamide, and acrylamide.
(42) A coating agent according to (38) or (39), wherein the binder contains an inorganic compound.
(43) A coating agent according to (42), wherein the inorganic compound is at least one species selected from the group consisting of a Zr compound, an Si compound, a Ti compound, and an Al compound.
(44) A method for forming a film exhibiting photocatalytic property, comprising applying a coating agent onto an object, and hardening the resultant film, wherein the film is hardened at a temperature of about 500xc2x0 C. or lower, and the coating agent is a coating agent as recited in any one of (38) through (43).
(45) A method for forming a film exhibiting photocatalytic property according to
(44), wherein the hardening temperature is about 200xc2x0 C. or lower.
(46) A method for forming a film exhibiting photocatalytic property according to (45), wherein the hardening temperature is about 30xc2x0 C. or lower.
(47) A product comprising a film exhibiting photocatalytic property, wherein the film is formed through a method as recited in any one of (44) through (46).
(48) A product comprising a film exhibiting photocatalytic property, characterized in that, in 5 L of dry air containing 60 ppm hydrogen sulfide, after the film having a surface area of 400 cm2 is irradiated with light for four hours by use of a day white fluorescent lamp such that the intensity of UV rays of 365 nm is 6 xcexcW/cm2, percent decomposition of the hydrogen sulfide is at least about 20%.
(49) A product according to (47) or (48), wherein the film exhibiting photocatalytic property has a thickness of about 0.01 to about 100 xcexcm.
(50) A product according to (49), wherein the film thickness is about 0.01 to about 0.1 xcexcm.
(51) A product according to (49), wherein the film thickness is about 1 to about 100 xcexcm.
(52) A product comprising a film exhibiting photocatalytic property according to (47) or (48), wherein, when transmittance at 550 nm in the absence of a film exhibiting photocatalytic property is represented by xe2x80x9cT1%,xe2x80x9d and transmittance at 550 nm in the presence of the film is represented by xe2x80x9cT2%,xe2x80x9d the product has a portion at which the ratio of T2/T1 is at least about 0.9.
(53) A product comprising a film exhibiting photocatalytic property according to (47) or (48), wherein, when light reflectivity at 550 nm in the absence of a film exhibiting photocatalytic property is represented by xe2x80x9cR1%,xe2x80x9d and light reflectivity at 550 nm in the presence of the film is represented by xe2x80x9cR2%,xe2x80x9d the product has a portion at which the ratio of R2/R1 is at least about 0.9.
(54) A product according to any one of (47) through (53), wherein the film exhibiting photocatalytic property has a pencil hardness of at least 2H.
(55) A product according to any one of (47) through (54), wherein, after the film exhibiting photocatalytic property is irradiated with light for 24 hours by use of a day white fluorescent lamp such that the intensity of UV rays of 365 nm is 6 xcexcW/cm2, the film has a contact angle of about 20xc2x0 or less with respect to water.
(56) A product according to (55), wherein the contact angle with respect to water is about 100 or less.
(57) A product according to (56), wherein the contact angle with respect to water is about 5xc2x0 or less.
(58) A product according to any one of (47) through (57), wherein, after the film exhibiting photocatalytic property is irradiated with light for 24 hours by use of a day white fluorescent lamp such that the intensity of UV rays of 365 nm is 6 xcexcW/cm2, and then allowed to stand in the dark for 24 hours, the film has a contact angle of about 20xc2x0 or less with respect to water.
(59) A product according to (58), wherein, after the film is allowed to stand in the dark for 24 hours, the film has a contact angle of about 10xc2x0 or less with respect to water.
(60) A product according to (59), wherein, after the film is allowed to stand in the dark for 24 hours, the film has a contact angle of about 5xc2x0 or less with respect to water.
(61) A product according to any one of (47) through (60), wherein, after the film exhibiting photocatalytic property is subjected for 4,000 hours to an acceleration-exposure test employing a xenon arc lamp, the film has a yellowing degree of about 10 or less, and after the film is irradiated with light for 24 hours by use of a day white fluorescent lamp such that the intensity of UV rays of 365 nm is 6 xcexcW/cm2, the film has a contact angle of about 20xc2x0 or less with respect to water.
(62) A product according to any one of (47) through (61), wherein the film exhibiting photocatalytic property is formed on an inorganic substrate.
(63) A product according to (62), wherein the inorganic substrate is of metal or ceramic.
(64) A product according to (62), wherein the inorganic substrate is at least one species selected from the group consisting of an Si compound and an Al compound.
(65) A product according to any one of (47) through (61), wherein the film exhibiting photocatalytic property is formed on an organic substrate.
(66) A product according to (65), wherein the organic substrate is an organic polymer.
(67) A product according to (66), wherein the organic polymer is at least one species selected from the group consisting of polyethylene, polypropylene, polystyrene, nylon 6, nylon 66, aramid, polyethylene terephthalate, unsaturated polyesters, polyvinyl chloride, polyvinylidene chloride, polyethylene oxide, polyethylene glycol, silicon resin, polyvinyl alcohol. vinylacetal resin, polyacetate, ABS resin, epoxy resin, vinyl acetate resin, cellulose derivatives such as cellulose and rayon, urethane resin, polyurethane resin, polycarbonate resin, urea resin, fluorine resin, polyvinylidene fluoride, phenol resin, celluloid, chitin, starch sheet, acrylic resin, melamine resin, and alkyd resin.
(68) A product according to any one of (62) through (67), which is at least one member selected from the group consisting of building materials, machinery, vehicles, glass products, electric appliances, agricultural materials, electronic apparatus, tools, tableware, bath products, toiletry products, furniture, clothing, cloth products, fibers, leather products, paper products, sporting goods, futon, containers, eyeglasses, signboards, piping, wiring, brackets, sanitary materials, and automobile parts.
(69) A method for imparting photocatalytic property and hydrophilicity to a product as recited in any one of (27), (28), and (68), wherein a light source employed for causing the product to exhibit photocatalytic property and hydrophilicity is at least one species selected from the group consisting of sunlight, a fluorescent lamp, a mercury lamp, a xenon lamp, a halogen lamp, a mercury xenon lamp, a metal halide lamp, a light-emitting diode, a laser, and flame obtained through combustion of an organic substance.